Thankfully, all 3 of our dogs carry 2 normal MDR1 genes. We know that thanks to DNA testing. Most MDR1 dog breeds with mutations come from the herding dog group of breeds, but the top list of breeds includes some surprises. I recently came across some stats on how common MDR1 mutations are in specific dog breeds.
Dogs have 2 MDR1 genes. Ideally, you want them both to come back Normal-Normal.
What Problems Does an MDR1 Dog Breeds Mutation Cause?
This gene mutation can lead to an increased chance of certain meds resulting on toxicity-type responses in the central nervous system due to dysfunction with the blood / brain barrier. This includes meds like:
- Butorphanol (analgesic)
- Acepromazine (sedative)
- Several antiparasitics (macrocyclic lactones), including the commonly available ivermectin
- Diarrhea and vomiting meds like loperamide and ondansetron.
The MDR1 mutation also affects some dogs ability to excrete some meds, including chemotherapy, via biliary excretion. This can lead to greater side-effects with drugs like these:
- Actinomycin D
- Cyclosporine (immunosupressant that our Mr. Stix takes for skin issues)
MDR1 Dog Breeds Approximate Frequency of Mutation
Here are the percentages as text to go with the bar chart above:
- 70% Collie
- 65% Windsprite (longhaired whippet)
- 50% Australian shepherds
- 30% McNab
- 30% Silken windhound
- 15% English shepherd
- 15% Shetland sheepdog
- 10% German shepherd dog
- 10% herding crossbreeds
- 5% crossbreeds
- 5% Old English sheepdog
- <5% Border collie
Honestly, I'm surprised the estimated frequency is so low in border collies and so high in Australian shepherds. It's also shocking to see a couple of sighthounds on the list.
What to do about MDR1 Dog Breeds Mutations?
Make sure your veterinarian knows about your dog's MDR1 mutations, if you find any after doing DNA screening tests. That way you can make decisions about drugs to avoid or drugs that require lower dosages for safe use for your dog.